1. Field of the Invention
This invention relates to electrosurgical devices. Electrosurgery is the application of a high-frequency electric current to tissue as a means to cut, coagulate, desiccate, or fulgurate tissue. Its benefits include the ability to make precise cuts with limited blood loss. Electrosurgery also includes surgical procedures where one or more localized portions of tissue are ablated using high frequency alternating current to generate heat, without heating other types of tissue near the target tissue. Electrosurgery devices use probe-like structures to physically contact the target tissue where such structure is a type of electrode acting to pass electrical current to the tissue. Electrosurgery devices typically cause substantial physical damage to tissue.
This invention applies an electrical field across target tissue, causing an electrical current to “conduct” across said target tissue. Heat is produced from this electrical current by ohmic or joule heating where the heat produced from such is proportional to the square of the amount of this current. A “lesion area” is created where tissue is heated above normal temperature. Heating occurs in a very controlled way where temperature of the lesion area does not rise above a maximum temperature. Carefully controlled heating provides the opportunity to cause a desired precise cell injury. The invention carefully controls heat generation in the lesion area with a self-limiting conductive material electrical component in electrical series connection with the electrical current in the target tissue. Self-limiting conductive material electrical component precisely controls the electrical current flowing across the target tissue.
Electrical current is directly proportional to heat production, which is directly proportional to temperature increase, where elevated temperature and duration of such, along with location and size of the lesion area, primarily determine the type and extent of cell damage, which, in turn, determines whether the desired precise cell injuries are attained. Thus, this invention uses precise current control to yield a precise minimum level of cell injury required to effect the desired result for the patient without going beyond this level, thereby effecting the result without unnecessary cell injury. All prior art electrosurgical devices and radio frequency medical devices cannot control temperature or heat production as precisely as this invention and thus cause more damage to target tissue.
The invention may be used in medical, dental, or veterinary applications. Exemplary embodiments of the invention have cosmetic applications including treatment of wrinkles and remodeling of subcutaneous tissue. Exemplary embodiments are also used for therapeutic applications including treatment of muscle spasmas and chronic pain and the control of one or more muscles of other target tissue. Exemplary embodiments are designed to specifically affect nerve tissue where the desired cell injury is to “deaden” the nerve or break the electrochemical connection, either temporarily or permanently, between nerve and muscle that causes nerve-to-muscle contractile function. However, this invention may be used to cause a desired precise cell injury to any type of cell or organ in the body within only the limitation of the relative sizes of the probes/needles on the invention apparatus as manufacturing technology changes with the times as compared to the size of the particular cells of interest, where cells may be of any type known human or otherwise.
2. Description of Related Art
A nerve is a cell that is relatively large. Each nerve cell contains a soma, multiple dendrites, an axon fiber, and multiple axon terminals. The soma is the central part of the nerve; it contains the nucleus of the cell. The soma can range from 4 to 100 micrometers in diameter. The axon and dendrites are filaments that extend outward from the soma. Many dendrites typically surround and branch off from the soma, and have length of up to a few hundred microns. The axon is a single cable-like projection extending outward from the soma that can extend over 100 times the diameter of the soma. The axon carries electrochemical nerve signals away from the soma to effectively control one or more muscles. Axon terminals are located opposite the soma-end of the axon. Typically, axon terminals terminate in a branch network of synapses, which release chemicals to communicate with one or more muscles or other tissue or with other dendrites or soma from another nerve cell within a chain of nerve cells leading to one or more muscles or other tissue.
Typically, a large number of axons from many cells are bundled together in a large conduit called an epineurium, with other nested conduits inside. Analyzing the physiological structure of these conduits, we start with an inner conduit or sheath called an endoneurium, which directly surrounds each axon. Multiple axons are typically grouped together into fasicles and further protected by a mid level sheath called a perineurium. Further, multiple perineurium bundles of axons are typically nested within an outer sheath called an epineurium. This is widely known in the art. Thus, each axon is protected by at least three sheath layers, i.e. an epineurium, a perineurium, and an endoneurium, going from outer most to innermost layer. Note that each large conduit or epineurium contains very many bundles of endoneurium conduits, thus it would be possible to sever completely the axons of some nerve cells, while leaving intact the complete endoneurium of other nerve cells.
This prompts a basic discussion of nerve cell injury. The Seddon system is a basic classification system used to describe nerve injury where there are three categories of injuries—neuropraxia, axonotmesis, and neurotmesis. The following is also well understood in the art.
With neuropraxia, the integrity of the axon is preserved so the endoneurium, perineurium, and epineurium are all intact, but there is an interruption in conduction of the electro-chemical impulse traveling down the axon. This is the mildest form of nerve injury. Neuropraxia is typically a biochemical lesion caused by concussion injuries to the cell. There is a temporary loss of function, which is reversible within hours to months of the injury (the average is 6-8 weeks).
With axonotmesis, the integrity of the axon is interrupted but the endoneurium, perineurium, and epineurium are not punctured or deformed significantly. The result is typically loss of both motor and sensory functions, but with recovery through regeneration of the axon, a process that takes place at a certain rate per day, typically taking longer than neuropraxia for recovery. With neuropraxia and axonotmesis the intact endoneurium provides a guide for axonal regeneration where the nerve regenerates along the endoneural tubules.
Conversely, with neurotmesis, the integrity of the supporting structures are disrupted or punctured, disrupting axonal regrowth and reimplantation. Typically, the injury results from severe contusion, stretch, or laceration of the cell or other internal disruption of the cell architecture sufficient to involve the perturbation of the endoneurium, perineurium, or epineurium. Results are typically complete loss of motor, sensory, and autonomic function. Thus, the electrochemical signals do not complete the connection to the muscle or target tissue. Neurotmesis injury is typically permanent.
Comparably, a temporary type of neurotmesis results from nerve toxicity caused by local anesthetic, which is typically injected in or near a nerve cell. Anesthetic also disrupts the electrochemical signals sent to the muscle, thereby causing a loss of motor, sensory, and autonomic function. Botulinum toxin or Botox®, as used with the popular cosmetic procedure for wrinkles, is used as a neuromodulator that works at the neuromuscular junction to block the transmission between the nerve and muscle resulting in paralysis of the muscle to reduce wrinkles.
This invention is first to provide the ability to effect a wide range of cell injury from a minimum level of neuropraxia to full neurotmesis, through electrical current heating means, without also effecting large-scale physical damage in the target area. This invention can provide temporary effects or permanent relief to a patient without surface tissue cosmetic defects.